Wave transmission system



3931; R. c. MATE-IE5 I WAVE TRANSMISSION SYSTEM Filed March 30, 1929 5Sheets-Sheet 1 .....,w. sq

Aug. 18,1931. R c.- MATHES WAVE TRANSMISSION SYSTEM Filed March 30, 19295 Sheets-Sheet 2 ATTORNEY R. c MATHES WAVE TRANSMISSION SYSTEM Aug.18,1931.

' s Sheets-Sheet 3 Filed March 30, 1929 A TTOFPNEY "5 sheet -sheet 4 R.c. Mma-ass WAVE TRANSMISSION 'SYSTEM Filed March 30,1929

Augo 18 A 7' TOHNEY Aug. 18, 1931. R. c. MATHES WAVE wnmsmss'xoiw sysTEMFiled March 30, 1929 5 Sheets-Sheet 5 ATTORNEY meme Aug. 18,1931

- UNITED STA ES PATENT. OFFICE ROBERT C. MATCHES, OF WYOMING, NEWJERSEY, ASSIGNOR TO BELL TELEPHONE LABO- RATORIES, INCORPORATED, OF NEWYORK, N. Y., A CORPORATION 01' NEW YORK wAvE rmsmssron SYSTEMApplication flied March 80, 1929. Serial No. 851,416.

This invention relates to wave transmission and especially to privacysystems of communication. I

' An object of the invention isto economize transmission delay apparatuswhere different delays are to be introduced in different trans- Imission channels.

A further object is to economize privacy apparatus.

In one specific form of the invention in which privacy in radiotelephony results from relatively delaying frequency bands of speechenergy in the general manner disclosed in Mathes Patent 1,542,566, June16, 1925, the

same delay apparatus is made to serve for both directions oftransmission in a two-way radio telephone system, and the total lengthof delay paths is economized by having one of two mutually'exclusivefrequency bands 2 of speech energy that are transmitted in the samedirection overthe system pass through two portions of a delay path intandem relationship, and having the other band passthrough one only ofthe two portions instead 1 5 of through a separate delay means of delaytime equal to that of the one portion.

, Other objects and features of the invention willbe apparent from thefollowing description and claims.

Fig. 1 shows a system embodying oneform of the invention; i

terminals, respective y, of a system embodying asecond form of theinvention; Fig.4

shows a terminal of a system embodying a third form of the invention;and Fig. 5 shows a terminal of a system embodying a fourth form of theinvention.

Fi 1 shows a four-wire type of-sy'stem, whic may be, for example, atelephone system transmitting speech between the twowire lines 1 andj2over the four-wire. portion of this circuit which includes line 3, fortransmission passing from line 1 to line 2, and line 5 for transmissionpassing from line 2 to line 1'." 'For convenience, line 1 may be desigs.2 and 3 show the two nated the west two-wire line, and line 2 the easttwo-wire line, the apparatus connecting line 1 with lines 3 and 4 beingdesignated the west terminal of the system and the apparatus connectinglline 2 with lines 3 and 4 being designated t e east terminal of thesystem. The use of dashes to represent lines 3 and 4-indicates that thelines may be of considerable extent and/or that a radio link or anydesired apparatus may be included in them.

- In the'system of Fig. 1 speech is divided into two frequency bands.The upper band is delayed on transmission from the west end, but thelower band is the one delayed on reception at that end. Thus, the mannerin which the speech is scrambled is the same for the two directions oftransmission. Consequently, more than two statlons can lntercom--municate with secrecy apparatus which is identically alike for each ofthe stations.

Starting from line 1 speech passing through bridgetransformer (hybridcoil) BT is divided into a lower frequency band and an upper frequencyband 'by a low pass filter 10 and a high pass filter 11. The lower bandpasses from filter 10 to line 3 without delay, and from line 3 throughlow pass filter 12, delay circuit or path 13, low pass filter 14,amplifier A-lfi, low pass filter 16, and bridge transformer ET on theline. 2. The upper band. passes from filter 11 through delay circuit orpath 20 of delay time equal to the delay. time of circuit 13, high passfilter 21,

amplifier A22, high pass filter 23, line 3, high pass' filter 24 ET onto line 2.

and bridge transformer by a low pass filter 30 and high pass filter 31.

The lower band passes from'filter 30 through line 4, low pass filter 32,delay path 20, low pass filter 33, amplifier A -34, low pass filter 35and bridge transformer BT on to line 1. The upper band passes fromfilter 31 through delay path 13, high pass filter 38, amplifier A39,high pass filter 40, line 4, high pass filter 41 and bridge transformerET on to line 1. All of the filters have the same cutoff frequency.

The feasibility of inserting the one-way amplifiers A-22 to A34 to makeup for the losses in the delay circuits facilitates the use of cheapforms of delay paths such as acoustic delay paths. 1

Figs. 2 and 3 show. a four-wire type of system generally similar to thatof Fig. 1, but differing in that the speech is divided into threefrequency bands instead oftwo, in order to increase the degree ofprivacy or seerecy obtained.- These three bands are desig nated 0F,, F Fand F oo Fig. 2 shows one terminal of the system, which for conveniencemay be designated the west terminal, and Fig. 3 shows the other or eastterminal. Y

The system will be sufiiciently described by tracing the operation atthe west and east ends of the circuit. Speech transmitted from west toeast passes from line 1 by way of the series winding of bridgetransformer (hy 'brid coil) BT to the junction of a high pass filter 50and a low pass filter 51. The pass ranges of the low pass, high pass andband pass filters, and the elimination ranges of the band eliminationfilters employed in Figs. 2, 3,4 and 5 of the drawingsare indicated onthe drawings. The half of the speech energy which passes by way of thebridge windings of the bridge transformer is lost in the receiving partof the circuit. The upper frequency band passes through the high passfilter 50, line3 of the four-wire transmitting part of the circuit. Thetwo lower bands pass through the low pass filter 51 and through delaycircuit or path 52 of delay time T. From the output of this delaycircuit the mid-band goes to the transmitting branch 3 of the four-wirecircuit through band pass filter 53 and is kept from going to delaycircuit or. path 54 by band elimination filter 55. The low frequencyband then passes through filter 55 to a branch of the four-wire circuitby way of delay path 54 of delay time T and low pass-filter 56.

On receiving by the circuit ofFig. 3 a sim-' ilar process takes placeexcept that the amounts of/delay are reversed as regards the lowfrequency band and the upper frequency band. Thus when speech from line3 passes to the junction of low pass filter 60, band pass filter 61 andhigh pass filter 62, the low lay circuit or'path 63 of delay time T,high pass filter 64'and bridge transformer ET on to line 2. The highfrequency band passesthrough filter 62. delay circuit or path 65 ofdelay time T, band elimination filter 66, and the delay path 63, filter64 and bridge transformer ET on to line 2.

Speech transmitted from line 2 passes by way of bridge transformer BT tothe junction of high pass filter 70, band pass filter 71 and low passfilter 72. The upper band passes through filter on to line 4. Themid-band passes. through filter 71, delay path 65 and low pass filter 73 on to line 4. The low band passes from filter 72, delay path 63,filter 66, delay path 65 and filter 7 3 011 to line 4.

On receiving at the west end of this sys- "tem by the circuit shown inFig. 2 a similar band. Thus speech from line 4 passes to the junction oflow pass filter 80 and high pass filter 81. The low band passes throughfilter 80 and bridge transformer ET on to line 1. The two upper bandspass through filter 81 and delay path 54. From the output of this delaypath the mid-band goes to bridge transformer BT and line 1 by way ofband pass filter 82 and is kept from going to delay circuit 52 by filter55. The high frequency band then passes to bridge transformer BT andline 1 by way of filter 55, delay path 52 and high pass filter 83.

No'transmission loss equalizers and amplifiers are shown in Figs. 2 and3 for making the overall transmission equivalent of the secrecyapparatus at each terminal the same and of the desired absolute value,for the three transmission bands, at each terminal of the system.However, a manner in which they can be applied to the system of thesefigures will be clear from the description hereinafter of Fig.5, whichshows a terminal circuit like that of Fig.2 but equipped with suchequalizers and amplifiers and with voice operated switching apparatus.Instead of using such equalizers and amplifiers there may be used, inthe circuits of any of the figures of the drawings, two-way delaycircuits of zero loss, or possible gain, such as are disclosed in ClarkPatent 1,672,057, June 5, 1928. or two-way electrical, mechanical oracoustic delay paths giving zero loss or a gain, such as are disclosedin my copending application, Serial No. 351,417 filed on even dateherewith.

Although the circuit shown. in Fig. 3, as the east terminal of thesystem, is slightly difi'erent from that shown in Fig. 2 as the westterminal, either circuit may be used for either or both terminals.

Fig. 4 shows one terminal, for convenience say the west terminal, ofatwo-wire type of system in which speech is divided into three bands, asin the case of the system of Figs. 1 and 2. The terminal circuit shownin Fig. 4 is a two-wire secrecy circuit which can have Lame zerotransmission loss, or can give again.

This 'circuit is derived from the terminal circuit shown in Fig. 2 bycoupling thetwo ff'filtBl' 122, low transmission loss equalizer 123,

four-wire parts of the circuit of Fig. 2 to-j gether Wlbh a bridgetransformer (hybrideo1l) and inserting the necessary amplifiers and"loss equalizers. The east terminal cor responding to the circuit'ofFig. 4 may sil'n'i larly be derived fromthe four-wiret'erminal of Fig.3; or if desired the east terminal may be the same as the west terminal.

' Theterminal circuit shown in Fig. 4 may be regarded as a two'wire-type repeater'cir- .cuit of zero loss or possible gain. -One"end"of this" circuit is connected to line 1.by bridge transformer (hybrid'coil') BT- and balancing network N. of-the usualtype, as in i the-easeof the terminal circuit of Fig. 2, and

' transformer BT on to dica'tes that it may be of considerable the otherend is connected to a two-way] secrecy line which transmits the signalsthat, have been so distorted as to be unintelligible. The use of dashesto represent this line 'inextent and/or that any desired apparatus, asfor example, the radio link mentioned in connection with the systems ofthe preceding figures may be included in the link between the twoterminals of the system.

The system will be sufliciently described by tracing the operation atthe west end. Transmission from west to east passes from line 1throughbridgetransformer BT and conductors 100 to the junction of highpass filter 101' and low pass filter 102. p The upper band passesthrough filter 101, transmisslon loss equalizer 103, high pass filter104-, conducto'rs 105, amplifier -106, the bridge line 1. The twolower.- bands pass through filter 102 and through delay circuit or path107' of delay time T. From the output of this delay path. the midbandpasses through band pass filter 108,

7 transmission loss equalizer 109','band pass tion by the west terminal.

v For transmission from east to west, speech from line 1 passes. throughbridgetransformer BT and conductors 115 to the junction of low passfilter 116 and high-pass filter 117. The low frequency band passes fromfilter 116 through transmission loss equalizer 118, low pass filter119.condu'ctors 120, amplifier'A-121 and bridge transformer ET on toline 1. The two upper bands alld pass through filter i117 and throughdelay path 112. From the output of this delay path the mid-band passesthrough band-pass me'11t s--may- -be' applied. Thus, for transmis- 'sionfrom west to east speech taken from conductors through conductors 130operates amplifier operates relays131 and 132. For transmission fromeast to west speech taken from conductors 115 through conductors 135operates amplifier rectifier Alt-136 which in turn 0prectifier AR-131which in turn era tes relays 137' and 138. Relay 131 opens conductors115, and relay 137 opens the conductors 100. By also having AR-131 openthe input circuit of A 121 at the contacts of relay 132 which areincluded in the conductors 120, and having Alia-136 open the inputcircuit of A--106 at contacts of relay 138 which are included intheconductors 105, the suppressor circuit will have characteristicspart-way between thoseof a two-wire suppressor circuit not provided withdelaycircuits and a two-wire suppressor circuit with delaycircuits asshown, for example, in Mathes Patent 1,693,955, December {1, 1928, or afour-wire echo suppressorcircuit of the type shown, for-example, in,Fig.,1 of E. D. Johnson Patent 1,526,550, February 17, 1925; for two bandsof the speech energy in the case of transmission in each direction aredelayed between the two hybrid coils, corresponding to the time delay inthe two halves of a four-wire circuit. Thusv reliability of operation isincreased and-the time during which circulating currents can build. upis reduced.

In circuits where voiceoperated repeater 7 switching is desired togetherwith conversion.

to secrecy, as for example, in the circuits at the two terminals of thepresent commercial trans-Atlantic radio telephone .system In which as inthe disclosure in Nyquist Patent 1,607,687, November 23, 1926) the'reserve to assist in reducing clipping or elim1'- ration of portions ofthe signals because of the time required to efiect switching. A way inwhich the voice operated control circuits and the delay circuit to avoidclipping on transmitting can be introduced is shown in Fig. 5 and willappear as the description of that figure proceeds.

Fig. 5 shows one terminal, for convenience say the west terminal, of afour-wire type of system which may be like that of Figs. 2 and 3, exceptfor the addition of voice operated switching means and the addition ofsuch amplifiers and transmission loss equalizers as are shown in Fig. 4.The two terminals may be the same, as regards contsruction andoperation. The system will be sufficiently described by explanation ofthe operation of the west terminal.

Speech energy starting from line 1 for delivery to line 3 passes throughbridge transformer BT and then divides into two portions, one of whichpasses through conductors 150 to amplifier-rectifier AR151 whichoperates relay 152 for opening a short circuit through its uppercontacts across line 3 and for opening the circuit through conductors154 at its lower contacts. The other portion passes through delaycircuit or path 156 of delay time T and then divides into a highfrequency band of range F w which passes through high pass filter 157,and a band 0F which passes through low pass filter 161. From filter 157the high frequency band passes through transmission loss e ualizer 158,high pass filter 159 and ampli er A160 on .to line 3. From filter 161the band 0F passes through delay circuit or path 162 of delay time T andis then separated by band pass filter. 163 and band elimination filter164 into mid-frequency band F F and low frequency band 0-,'F Themid-band F F after passing through filter 163, goes through transmissionloss equalizer 165, band pass filter 166 and amplifier A16O on to line3. The low band 0F after passing through filter 164, goes through delaycircuit or path 167 of delay time T, low'pass filter 168 and amplifierA160 on to line 3.

The operation of receiving at the east terminal may be the same as atthe west terminal, and so will be apparent from-the explanation now to.be given of the latter operation.

Speech energy coming from line 4 for delivery to line 1 passes throughthe lower contacts of relay 152, which are included in conductors 154.and then divides into two portions, one of which passes throughconductor 170 to amplifier-rectifier AR171 which operates relay 172 foropening the circuit of AR151 to prevent false operation of AR 151 byunbalance-currents or echo currents received from the bridge points ofthe bridge transformer ET. The other portion divides I into a lowfrequency band of range 0-F which passes through low pass filter 175,and a band F -oo which passes through high pass filter 176. From filter175 the low frequency hand passes through transmission loss equalizer177, low pass filter 178, amplifier A179 and bridge transformer BT onpassing through filter 180, goes through transmission loss equalizer181, band pass filter 182, amplifier A.179 and bridge transformer ET onto line 1. The high frequency band F w, after passing through filter164, goes through delay path 162. high pass filter 183, amplifier A17 9and bridge transformer BT onto line 1.

The control circuit fed from the. bridge points of the bridgetransformer BT through conductors 150 does two things. It opens a shortcircuit on the output side of theampl fier A160 that transmits to thesending line 3; audit disconnects the terminal from'the receiving line 4and thereby prevents operation of the receiving amplifier-rectifier AR171 in the other control circuit, fed from line 4 through conductors 154and 170. The

latter control circuit opens the control circuit fed from the bridgepoints of the bridge transformer. The delay time T introduced by delaypath 156 prevents clipping of the energy of the upper frequency band.The energy of the two lower frequency bands has additional timedelayprotection, of timesT and 2T, against clipping.

In the circuit of Fig. 5, as well as in that of Fig. 4, the transmissionloss equalizers shown may be given such losses, and the amplifiers shownmay be given such gains, as to cause the overall transmission loss orgain for the three frequency bands, through the circuit, to be the same,and of the desired value;

Where desired the delay paths in any of the systems described herein maybe of the mechanical or acoustic types instead of electrical delaycircuits. Examples of electrical, mechanical and acoustical delay pathsthat may be employed in these systems are disclosed in Mathes patent1,696,315, December 25, 1928.

What is claimed is:

1. In combination, a wave transmission path, a second wave transmissionpath, a third Wave transmission path, two transmission delay paths, andmeans for transmitting selected waves between said first and secondpaths through said delay paths in tandem, to the exclusion of otherwaves, and transmitting said other waves between said first and thirdpaths through one, only, of said delaypaths.

2. Means for altering the time relation of waves transmittedtherethrough, comprisping paths in opposite directions through saidmeans, said paths in opposite directions havmg portions least common,transmission delay means included 1n sald common portions,

and means for transmitting waves of certam frequencies through each oftwo portions of said delay means and transmitting ing paths in oppositedirections through said means, said paths in opposite directions havingportions at least common, transmission delay means included in saidcommon portions, and means, including filters, for transmitting waves ofcertain frequencies through each of two portions of said delay means intandem relationship and transmitting waves of other frequencies in agiven direction through one only of said two portions.

4. Means for altering the time relation of waves transmittedtherethrough, comprising paths in opposite directions through saidmeans, said paths in opposite directions having portions at leastcommon, transmission delay means included in said common portions, andmeans, including a band elimination filter, for transmitting certainfrequencies in one direction only through both of two portions of saiddelay means in tandem relationship and transmitting other frequencies inonly the opposite direction through both of said two portions andtransmitting still other frequencies in one direction only ing said twocircuits to said line in conjugate relation to each other, and meansconnected in said two circuits for altering the time relation of wavestransmitted there through, comprising, in combination, paths in oppositedirections through said means,

said paths in opposite directions having portions at least common,transmission delay means included in said common portions, and

means, including filters, for transmitting waves of certain frequenciesthrough each transmission of those signals in the opposite direction inthe system, means for relatively delaying frequency bands ofenergy ofsaid signals, and a delay path common to said two means, said means forrelatively delaying the frequency bands comprising, in combination, awave transmission path, a second .wave transmission path, a third wavetransmission path, two transmission delay paths, and means fortransmitting selected waves between said first and second wave transmission paths through the two last mentioned delay paths in tandem, tothe ex clusion of other, waves, and transmitting said other wavesbetween said first and third wave transmission paths through one, only,of the two latter delay paths.

In witness whereof, I hereunto-subscribe my name this 27th day of March,1929.

ROBERT-C. MATHES.

